1. Field of the Invention
The present invention relates to optical character readers and to the processing of signals, such as video signals, produced by an image scanner of a character reader as the face of a document passes by. More particularly, the invention relates to a system for processing video signals from a scanner in a manner which enhances the signals so that they more accurately represent characters being read from the document.
2. Description of the Prior Art
Exemplary prior art relating to signal processors for improving the performance of optical scanners may be found in patents which have issued in the United States.
Among these United States patents are U.S. Pat. No. 4,162,481 to Du Vall which issued on July 24, 1979. Du Vall discloses a technique which resembles, in part, that of the present invention; but, he uses his apparatus to determine when an improper reference background exists and then alters parameters to correct for the background. The method and apparatus for enhancing images according to the present invention are patentably distinct over Du Vall in that enhancement is directed to an individual pixel of a character relative to a matrix of pixels of the character rather than to improvement against the background as such. In addition to the foregoing distinctions, the apparatus employed and the procedures followed in attaining the results of the present invention are different and are patentably distinct over those shown by Du Vall.
Other U.S. patents which are of interest are U.S. Pat. No. 3,747,066 to Vernot which issued on July 17, 1973 and U.S. Pat. No. 4,119,947 to Leighton, et al which issued on Oct. 10, 1978. Each of these patents relates to signal processors for optical scanners which embody the idea of comparing a small area with a larger surrounding area with the object of generating signals to help identify part of a printed character or other pattern. Neither anticipates the present invention as set forth in the claims.
The broad idea of comparing the brightness of a small portion of a scanned document to the brightness of an ambient gray area around that portion to provide a basis for correcting or enhancing signals relating to a character being scanned is shown in the literature. Reference may be made to the IEEE Transactions on Computers for February, 1974 entitled "Black-White Representation of a Gray-Scale Picture". The present invention, as claimed, is believed to distinguish patentably over that reference.